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Bisagno river diversion (Italy)


Project: Flood control works on the Bisagno River

Location: Liguria Region, Italy

Client: Provincial administration of Genova

Cost of total Works: 153.427.629 €

Services: Final Design

Period: 2003 - 2008

In the first years of 2000, occurred some flooding events in the Genova area. Some studies conducted by local River Basin Autority emphasized the risk of flooding of Genova by the Bisagno River and the Ferragiano, Rovare and Noce streams.

To solve this situation the River Authority has provided a series of measures to minimize the risk of flooding of large areas currently occupied by urban settlements.
Among the main changes is expected to:
  • expand the river section in the most critical stretch
  • build a drainage canal, to reduce the peak discharges flowing in the original riverbed
Technital was involved (in Temporary Association with SGI Studio Galli, Studio Maione and Sogreah) to design the drainage canal.
The project of the river diversion, for the Bisagno River, includes the following works:
  • a river barrage equipped with n. 3 radial gates
  • a tunnel, with a horseshoe section with 9.5 m diameter, able to carry to the Tirreno sea, a portion of the flood discharges derived by a lateral weir; the tunnel is 6’650 m long
  • three smaller diversion structures on the Fereggiano, Rovare and Noce streams, connected to the main tunnel through three tunnels 300 m long
  • a sea outfall structure of the main tunnel
  • two service tunnels
The design was based on the results of physical models made by Sogreah Laboratory under described.
The main interventions are as follow:
  • the work of the dam: it consists of a cross with three spans of equal wide and controlled by three gates, other complementary works are: a building command and control, a building for the housing of the planks, and two runways service;
  • the intake: it consists of a lateral spillway, with overflow Creager type profile, placed in the frieze to the left bank of the stream, variable width, connected to the main water supply;
  • intervention on the riverbed: includes construction of a bridle, reinforced concrete, placed 200 m upstream of the dam, the reshaping of the riverbed trapezoidal cross-section for the entire section occupied by the works, and a series of thresholds for the bottom in reinforced concrete;
  • pedestrian walkway: since the realization of the works involved the demolition of the existing footbridge, 350 m upstream of the bridge, Ugo Gallo has planned to realize a new bridle foot bridge in correspondence of the new bridle above described.
Further specific information
The main gallery allows conveying to the sea the flood waters derived from the intake works.
The total length is about 7000 m and the polycentric section has a diameter of 9.5 meters.
The galleries from the intake works on Fereggiano, Rovare e Noce streams have a total length of 300 m and a diameter of 5 m.
In order to check the hydraulic behaviour of the major works, some tests were performed on a physical model, with regard to:
Work of dam and power.
The tests, that were conducted by a physical model of the work carried out on the dam of the Bisago River and on the intake, were divided into two series: the first one involved the examination of the hydraulic behaviour of the work under a "fixed bed", and the second one under “mobile bed” conditions.
Confluence between the main gallery and the gallery coming from the Fereggiano River.
the tests conducted by the model have been aimed at determining the effects of the confluence of the two galleries on the motion that occurs in the main gallery. In particular it was intended to observe the stationary disturbances that arise at the confluence, the possible formation of hydraulic jumps, and the possibility that the main gallery going under pressure because of the losses generated by the confluence itself.
Work on the sea outfall.
The tests allowed to determine:
  • the waves and the hydrodynamic currents in front of the mouth
  • the stability of land cliff in the absence of any bulwark at sea
  • the hydrodynamic conditions at the outfall for high flow rates exiting the scolmatore
  • evaluation of the stresses determined by the extreme waves on the structure

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  • Bisagno-1 Bisagno-1
  • Bisagno-2 Bisagno-2